ESP WebSocket Client¶
Overview¶
The ESP WebSocket client is an implementation of WebSocket protocol client for ESP32
Features¶
Supports WebSocket over TCP, TLS with mbedtls
Easy to setup with URI
Multiple instances (Multiple clients in one application)
Configuration¶
URI¶
Supports
ws
,wss
schemesWebSocket samples:
ws://echo.websocket.org
: WebSocket over TCP, default port 80wss://echo.websocket.org
: WebSocket over SSL, default port 443
Minimal configurations:
const esp_websocket_client_config_t ws_cfg = {
.uri = "ws://echo.websocket.org",
};
The WebSocket client supports the use of both path and query in the URI. Sample:
const esp_websocket_client_config_t ws_cfg = {
.uri = "ws://echo.websocket.org/connectionhandler?id=104",
};
If there are any options related to the URI in
esp_websocket_client_config_t
, the option defined by the URI will be
overridden. Sample:
const esp_websocket_client_config_t ws_cfg = {
.uri = "ws://echo.websocket.org:123",
.port = 4567,
};
//WebSocket client will connect to websocket.org using port 4567
TLS¶
Configuration:
const esp_websocket_client_config_t ws_cfg = {
.uri = "wss://echo.websocket.org",
.cert_pem = (const char *)websocket_org_pem_start,
};
Note
If you want to verify the server, then you need to provide a certificate in PEM format, and provide to cert_pem
in websocket_client_config_t
. If no certficate is provided then the TLS connection will to default not requiring verification.
PEM certificate for this example could be extracted from an openssl s_client command connecting to websocket.org.
In case a host operating system has openssl and sed packages installed, one could execute the following command to download and save the root or intermediate root certificate to a file (Note for Windows users: Both Linux like environment or Windows native packages may be used).
`
echo "" | openssl s_client -showcerts -connect websocket.org:443 | sed -n "1,/Root/d; /BEGIN/,/END/p" | openssl x509 -outform PEM >websocket_org.pem
`
This command will extract the second certificate in the chain and save it as a pem-file.
Subprotocol¶
The subprotocol field in the config struct can be used to request a subprotocol
const esp_websocket_client_config_t ws_cfg = {
.uri = "ws://websocket.org",
.subprotocol = "soap",
};
Note
The client is indifferent to the subprotocol field in the server response and will accept the connection no matter what the server replies.
For more options on esp_websocket_client_config_t
, please refer to API reference below
Events¶
WEBSOCKET_EVENT_CONNECTED: The client has successfully established a connection to the server. The client is now ready to send and receive data. Contains no event data.
WEBSOCKET_EVENT_DISCONNECTED: The client has aborted the connection due to the transport layer failing to read data, e.g. because the server is unavailable. Contains no event data.
WEBSOCKET_EVENT_DATA: The client has successfully received and parsed a WebSocket frame. The event data contains a pointer to the payload data, the length of the payload data as well as the opcode of the received frame. A message may be fragmented into multiple events if the length exceeds the buffer size. This event will also be posted for non-payload frames, e.g. pong or connection close frames.
WEBSOCKET_EVENT_ERROR: Not used in the current implementation of the client.
If the client handle is needed in the event handler it can be accessed through the pointer passed to the event handler:
esp_websocket_client_handle_t client = (esp_websocket_client_handle_t)handler_args;
Limitations and Known Issues¶
The client is able to request the use of a subprotocol from the server during the handshake, but does not do any subprotocol related checks on the response from the server.
Application Example¶
A simple WebSocket example that uses esp_websocket_client to establish a websocket connection and send/receive data with the websocket.org server can be found here: protocols/websocket.
Sending Text Data¶
The WebSocket client supports sending data as a text data frame, which informs the application layer that the payload data is text data encoded as UTF-8. Example:
esp_websocket_client_send_text(client, data, len, portMAX_DELAY);
API Reference¶
Functions¶
-
esp_websocket_client_handle_t
esp_websocket_client_init
(const esp_websocket_client_config_t *config)¶ Start a Websocket session This function must be the first function to call, and it returns a esp_websocket_client_handle_t that you must use as input to other functions in the interface. This call MUST have a corresponding call to esp_websocket_client_destroy when the operation is complete.
- Return
esp_websocket_client_handle_t
NULL if any errors
- Parameters
[in] config
: The configuration
-
esp_err_t
esp_websocket_client_set_uri
(esp_websocket_client_handle_t client, const char *uri)¶ Set URL for client, when performing this behavior, the options in the URL will replace the old ones Must stop the WebSocket client before set URI if the client has been connected.
- Return
esp_err_t
- Parameters
[in] client
: The client[in] uri
: The uri
-
esp_err_t
esp_websocket_client_start
(esp_websocket_client_handle_t client)¶ Open the WebSocket connection.
- Return
esp_err_t
- Parameters
[in] client
: The client
-
esp_err_t
esp_websocket_client_stop
(esp_websocket_client_handle_t client)¶ Stops the WebSocket connection without websocket closing handshake.
This API stops ws client and closes TCP connection directly without sending close frames. It is a good practice to close the connection in a clean way using esp_websocket_client_close().
Notes:
Cannot be called from the websocket event handler
- Return
esp_err_t
- Parameters
[in] client
: The client
-
esp_err_t
esp_websocket_client_destroy
(esp_websocket_client_handle_t client)¶ Destroy the WebSocket connection and free all resources. This function must be the last function to call for an session. It is the opposite of the esp_websocket_client_init function and must be called with the same handle as input that a esp_websocket_client_init call returned. This might close all connections this handle has used.
Notes:
Cannot be called from the websocket event handler
- Return
esp_err_t
- Parameters
[in] client
: The client
-
int
esp_websocket_client_send
(esp_websocket_client_handle_t client, const char *data, int len, TickType_t timeout)¶ Generic write data to the WebSocket connection; defaults to binary send.
- Return
Number of data was sent
(-1) if any errors
- Parameters
[in] client
: The client[in] data
: The data[in] len
: The length[in] timeout
: Write data timeout in RTOS ticks
-
int
esp_websocket_client_send_bin
(esp_websocket_client_handle_t client, const char *data, int len, TickType_t timeout)¶ Write binary data to the WebSocket connection (data send with WS OPCODE=02, i.e. binary)
- Return
Number of data was sent
(-1) if any errors
- Parameters
[in] client
: The client[in] data
: The data[in] len
: The length[in] timeout
: Write data timeout in RTOS ticks
-
int
esp_websocket_client_send_text
(esp_websocket_client_handle_t client, const char *data, int len, TickType_t timeout)¶ Write textual data to the WebSocket connection (data send with WS OPCODE=01, i.e. text)
- Return
Number of data was sent
(-1) if any errors
- Parameters
[in] client
: The client[in] data
: The data[in] len
: The length[in] timeout
: Write data timeout in RTOS ticks
-
esp_err_t
esp_websocket_client_close
(esp_websocket_client_handle_t client, TickType_t timeout)¶ Close the WebSocket connection in a clean way.
Sequence of clean close initiated by client:
Client sends CLOSE frame
Client waits until server echos the CLOSE frame
Client waits until server closes the connection
Client is stopped the same way as by the
esp_websocket_client_stop()
Notes:
Cannot be called from the websocket event handler
- Return
esp_err_t
- Parameters
[in] client
: The client[in] timeout
: Timeout in RTOS ticks for waiting
-
esp_err_t
esp_websocket_client_close_with_code
(esp_websocket_client_handle_t client, int code, const char *data, int len, TickType_t timeout)¶ Close the WebSocket connection in a clean way with custom code/data Closing sequence is the same as for esp_websocket_client_close()
Notes:
Cannot be called from the websocket event handler
- Return
esp_err_t
- Parameters
[in] client
: The client[in] code
: Close status code as defined in RFC6455 section-7.4[in] data
: Additional data to closing message[in] len
: The length of the additional data[in] timeout
: Timeout in RTOS ticks for waiting
-
bool
esp_websocket_client_is_connected
(esp_websocket_client_handle_t client)¶ Check the WebSocket client connection state.
- Return
true
false
- Parameters
[in] client
: The client handle
-
esp_err_t
esp_websocket_register_events
(esp_websocket_client_handle_t client, esp_websocket_event_id_t event, esp_event_handler_t event_handler, void *event_handler_arg)¶ Register the Websocket Events.
- Return
esp_err_t
- Parameters
client
: The client handleevent
: The event idevent_handler
: The callback functionevent_handler_arg
: User context
Structures¶
-
struct
esp_websocket_event_data_t
¶ Websocket event data.
Public Members
-
const char *
data_ptr
¶ Data pointer
-
int
data_len
¶ Data length
-
uint8_t
op_code
¶ Received opcode
-
esp_websocket_client_handle_t
client
¶ esp_websocket_client_handle_t context
-
void *
user_context
¶ user_data context, from esp_websocket_client_config_t user_data
-
int
payload_len
¶ Total payload length, payloads exceeding buffer will be posted through multiple events
-
int
payload_offset
¶ Actual offset for the data associated with this event
-
const char *
-
struct
esp_websocket_client_config_t
¶ Websocket client setup configuration.
Public Members
-
const char *
uri
¶ Websocket URI, the information on the URI can be overrides the other fields below, if any
-
const char *
host
¶ Domain or IP as string
-
int
port
¶ Port to connect, default depend on esp_websocket_transport_t (80 or 443)
-
const char *
username
¶ Using for Http authentication - Not supported for now
-
const char *
password
¶ Using for Http authentication - Not supported for now
-
const char *
path
¶ HTTP Path, if not set, default is
/
-
bool
disable_auto_reconnect
¶ Disable the automatic reconnect function when disconnected
-
void *
user_context
¶ HTTP user data context
-
int
task_prio
¶ Websocket task priority
-
int
task_stack
¶ Websocket task stack
-
int
buffer_size
¶ Websocket buffer size
-
const char *
cert_pem
¶ Pointer to certificate data in PEM or DER format for server verify (with SSL), default is NULL, not required to verify the server. PEM-format must have a terminating NULL-character. DER-format requires the length to be passed in cert_len.
-
size_t
cert_len
¶ Length of the buffer pointed to by cert_pem. May be 0 for null-terminated pem
-
const char *
client_cert
¶ Pointer to certificate data in PEM or DER format for SSL mutual authentication, default is NULL, not required if mutual authentication is not needed. If it is not NULL, also
client_key
has to be provided. PEM-format must have a terminating NULL-character. DER-format requires the length to be passed in client_cert_len.
-
size_t
client_cert_len
¶ Length of the buffer pointed to by client_cert. May be 0 for null-terminated pem
-
const char *
client_key
¶ Pointer to private key data in PEM or DER format for SSL mutual authentication, default is NULL, not required if mutual authentication is not needed. If it is not NULL, also
client_cert
has to be provided. PEM-format must have a terminating NULL-character. DER-format requires the length to be passed in client_key_len
-
size_t
client_key_len
¶ Length of the buffer pointed to by client_key_pem. May be 0 for null-terminated pem
-
esp_websocket_transport_t
transport
¶ Websocket transport type, see `esp_websocket_transport_t
-
char *
subprotocol
¶ Websocket subprotocol
-
char *
user_agent
¶ Websocket user-agent
-
char *
headers
¶ Websocket additional headers
-
int
pingpong_timeout_sec
¶ Period before connection is aborted due to no PONGs received
-
bool
disable_pingpong_discon
¶ Disable auto-disconnect due to no PONG received within pingpong_timeout_sec
-
bool
use_global_ca_store
¶ Use a global ca_store for all the connections in which this bool is set.
-
bool
skip_cert_common_name_check
¶ Skip any validation of server certificate CN field
-
bool
keep_alive_enable
¶ Enable keep-alive timeout
-
int
keep_alive_idle
¶ Keep-alive idle time. Default is 5 (second)
-
int
keep_alive_interval
¶ Keep-alive interval time. Default is 5 (second)
-
int
keep_alive_count
¶ Keep-alive packet retry send count. Default is 3 counts
-
size_t
ping_interval_sec
¶ Websocket ping interval, defaults to 10 seconds if not set
-
const char *
Enumerations¶
-
enum
esp_websocket_event_id_t
¶ Websocket Client events id.
Values:
-
WEBSOCKET_EVENT_ANY
= -1¶
-
WEBSOCKET_EVENT_ERROR
= 0¶ This event occurs when there are any errors during execution
-
WEBSOCKET_EVENT_CONNECTED
¶ Once the Websocket has been connected to the server, no data exchange has been performed
-
WEBSOCKET_EVENT_DISCONNECTED
¶ The connection has been disconnected
-
WEBSOCKET_EVENT_DATA
¶ When receiving data from the server, possibly multiple portions of the packet
-
WEBSOCKET_EVENT_CLOSED
¶ The connection has been closed cleanly
-
WEBSOCKET_EVENT_MAX
¶
-